1. Field of the Invention
The invention relates to a method of capturing image data for iris code based identification of vertebrates, including humans, the method comprising the steps of:                recording a digital image of an eye with a camera equipped with at least two light sources that have a fixed spatial relationship to an object lens of the camera; and        locating the eye in the digital image by detecting a specularity pattern that is created by reflection of light from said at least two light sources at a cornea of the eye.        
2. Description of Background Art
A method of this type has been described in US 2007/0140531 A1 and is used in the context of biometric identification systems based on iris analysis.
A biometric personal identification system based on iris analysis has been described by John G. Daugman in U.S. Pat. No. 5,291,560 and in J. G. Daugman: “How Iris Recognition Works”, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 14, no. 1, pp. 21-30, January 2004.
Such identification systems take advantage of the fact that the iris of the eye of an individual, which may be a human or a vertebrate, has a characteristic pattern that is unique for that particular individual, so that an iris analysis may be used for uniquely identifying the individual. To that end, an image of an eye of the individual is captured with a digital camera, and image processing algorithms are used for recognizing the pupil and the iris of the eye in the digital image. Then, the iris pattern is normalized so as to compensate the effect of varying dilation or contraction of pupil, and a filter procedure is employed for transforming the normalized image of the iris into a digital code, a so-called iris code, that is unique to the individual and may therefore be used for identification purposes.
Once an iris code of an individual has been created and stored, that individual may be identified by capturing again an image of its eye, creating an iris code on the basis of the new image, and checking the iris code thus obtained against the code that had been stored previously.
In the image capturing method that has been specified in the opening paragraph, the recognition of the eye, especially its pupil and iris, is facilitated by detecting the specular reflection that is created by reflection of light from the light sources at the cornea of the eye. When, for example, the camera is equipped with two light sources, the specularity pattern will consist of two neighboring bright spots which can easily be identified in the digital image and the positions of which will roughly correspond to the position of the pupil of the eye, when the image has been captured head-on with the camera.
In order for the image data and the iris codes derived therefrom to be comparable, the images of the eye should be captured under similar, preferably identical conditions. Ideally, the camera should always have the same distance from the eye when the image is taken, and it should also be aligned on the “line of sight” of the eye, i.e. the line that passes through the center of the pupil and is normal to the plane of the pupil.